This invention relates to a process of producing a composite cast article having a polymeric solid surface with added filler and a backing of similar material also filled with hollow bubbles, with no transition zone of unfilled polymer between the layers.
Solid surface materials are known in the art including those based on polymethyl methacrylate and alumina trihydrate. Basic technology for these products is disclosed in U.S. Pat. No. 3,847,865xe2x80x94Duggins (1974), U.S. Pat. No. 4,085,246xe2x80x94Buser, Roedel and Vassiliou (1978), and published PCT patent application U.S. Ser. No. 88/04322xe2x80x94Frank, Otremba; Pohl and Schlier (1988).
Prior attempts to laminate such solid surface materials with bubble-filled backing material and fiberglass-reinforcement have led to expensive multi-step processes and to laminar products which had distinctly different layers with their own properties. Laminar products generally are more prone to delamination and other weaknesses due to the interface under certain conditions than integral products. Among the multi-layer, laminated products of this type is that of EP 285,046xe2x80x94Schock (1993).
All of the above-mentioned documents are incorporated herein by reference for their teachings of methods and materials for making solid surface filled polymeric materials. It would be desirable to be able to provide lighter weight sheet material with the surface characteristics of this solid surface material in integral form without laminar transitions between layers, and to be able to prepare such products by less expensive processes.
The present invention provides a process of producing the cast composite article comprising a polymer matrix and two zones of different filler, said article being substantially flat with two opposing faces, a first zone of such article including one face of the article having filler at a level in the range of 10 to 80% by weight of the filler plus matrix, and a second zone including the second face opposing said first face having filler of 5 to 60% and 3 to 30% of bubbles, both by weight of the filler and bubbles plus matrix, said first and second zones forming a continuum with essentially no layer of unfilled matrix between the two zones. Said process comprising the steps of forming a multi-layer composite article by casting on a flat surface a first mix comprising the polymerizable monomer(s) and a filler which will cure to give the composition of said first zone, and, before said first mix cures substantially, casting on the first mix a second mix comprising polymerizable monomer(s), filler, and bubbles which will cure to give the composition of said second zone, under conditions that will cause the second mix and the first mix to interpenetrate, so that there is essentially no interface in the matrix and no resulting layer of unfilled polymer, and curing the resulting composite article. In other embodiments, a third layer is added to the second layer, having a composition in the limits of the first layer. Also, a hard face can be added by applying it before the first layer with a filler harder than ATH, such as alumina, silica, calcium carbonate, or natural stone material such as granite. Furthermore, ground particles of filled or unfilled resin can be added to the first layer in accordance with the ground particles taught in U.S. Pat. No. 4,085,246.